I. Field of the Invention
The present invention relates generally to the field of chemistry and catalysis. More particularly, it relates to phospho-amino pincer-type ligands, metal complexes thereof, and catalytic methods comprising such metal complexes.
II. Description of Related Art
Pincer-type transition metal complexes have been studied in the last decade (Jensen, 2007; van der Boom and Milstein, 2003). The pincer ligand systems provide a number of desirable properties. They can coordinate to metal to form metallocycles with excellent thermal stability and the reactivity of these complexes have been found to vary with the structure/substituent of the pincer ligands. Moreover, pincer-type transition metal complexes have found useful applications in many fields, especially in catalysis, including for the catalytic hydrogenation of carbon dioxide (Tanaka et al., 2009), catalytic dehydrogenation of alkane (Gupta et al., 1996; Gupta et al., 1997; Xu et al., 1997; Liu et al., 1999; Haenel et al., 2001; Ray et al., 2005; Goldman et al., 2006), catalytic hydrogenation of ketone (Langer et al., 2011), or direct synthesis of amides from alcohols and amines (Gunanathan et al., 2007; Milstein et al., 2008; Gnanaprakasam et al., 2010; Gunanathan et al., 2010; Milstein, 2010; Gnanaprakasam and Milstein, 2011). In view of these advances, it would be desirable to develop new pincer-type ligands having different properties or profiles from those already known. If successful, such attempts would provide a greater palette of such ligands, which would expand the options available to a chemist, for example, to allow the best ligand to be selected for given application and/or to extend the use of these ligands to new applications. Similar considerations apply to metal catalysts comprising such ligands, as well as methods of using such metal catalysis. Therefore new pincer-type ligands, especially a novel class of these ligands, and transition metal complexes thereof would be a great advantage.